1. Field of the Invention
The present invention relates to a power unit for air conditioning systems principally intended for installation on boats.
2. Discussion of Related Art
The air conditioning system is a common system on board of cabin cruisers, also of medium-small size, and is now considered essential by almost all boat owners, at least in hotter areas of the world.
Depending on the type of boat, systems having different concepts can be used. However, even for the smallest boats (i.e. with only one room to be cooled) the energy source remains the electrical current, which is generated by a generator set or by the shore power line if the boat is in port. This activates an electric motor, which drives the compressor of the cooling device.
In the case of boats of larger dimensions, with more than one room (or cabin) to be cooled, centralized systems are installed. These can be of two types: with direct distribution of coolant gas to the evaporators or with circulation of treated water, i.e. previously cooled by a refrigeration device through a heat exchanger, sent to one or more fan coils.
In any case, all air conditioning systems available on the market require the presence of a generator set capable of supplying the necessary power for an electrically operated compressor.
In fact, in air conditioning systems installed on boats, the compressor is a device operated by an electric motor, which, owing to the fact that it can also be powered directly by the shore power network, requires an alternating current power supply.
The rated installed power of the compressor (conventionally indicated with the unit of measure BTU/h) depends on the size of the system, i.e. on its characteristic parameters, namely the volume to be cooled, the difference in temperature to be imparted and the coolant fluid used (i.e. its specific heat).
The electrical power required by the compressor motor, as already mentioned, is normally supplied by the electric generator of a generator set installed for this purpose, which must also supply the accessories of the system, such as the water circulation pumps and the fan coil fans. Alternatively, when the boat is moored in an appropriately equipped port, the power supply to the compressor motor and to the aforesaid accessories can be provided by the shore power network.
Nonetheless, due to the high cost and considerable weight, a generator set capable of supplying utilities with alternating current is rarely present on small and medium sized pleasure boats, where the on board batteries charged by the alternators of the main motors are generally sufficient.